1. Field of the Invention
This invention relates to the field of discrete power device and integrated circuit (IC) contacts, and particularly to contacts for use on silicon carbide (SiC) substrates.
2. Description of the Related Art
Electrical contacts are used to enable electrical signals to be conveyed into and out of a semiconductor device. Such contacts include a metal layer. When the voltage across and the current through the metal-semiconductor junction has a linear current-voltage (I–V) relationship, the contact is referred to as an “ohmic” contact. When the contact's I–V relationship has the characteristics of a forward-biased diode, the contact is referred to as a Schottky contact.
Silicon carbide (SiC) is a semiconductor material which is becoming increasingly popular, particularly for high power applications. Ohmic contacts to n-type SiC are conventionally provided using a metal layer of nickel (Ni), while aluminum/titanium (Al/Ti), Ti, or Al/Ni are generally used with p-type SiC. Schottky contacts are conventionally provided with Ni or Ti or others for n-type or p-type SiC.
Unfortunately, contacts for SiC-based devices present certain difficulties, particularly with respect to ohmic contacts. Conventional ohmic contacts on SiC as described above require a high temperature (>1050° C.) annealing step to obtain low specific contact resistance (a parameter related to a contact's resistance versus its area). This annealing step can cause the formation of a carbon-rich interface between the SiC substrate and the metal, which can result in poor adhesion for the metal, and degraded device reliability. In addition, the high temperature at which the annealing process is performed may cause other device parameters to be degraded, such as the channel mobility for MOS-gate based devices.